Strange duplication of ModelBones across instances of objects using the model - xna

Question

This is the first question I have asked, I'll try and keep this brief and detailed.
Basically, I am trying to create randomized cars made from a selection of models. I have 5 of each model part: Chassis, Engine, Spoiler and Wheels. The randomizer is working, models are loading. However, there is an issue where models are being drawn on other models. Usually there are only small parts of the model being drawn on other parts.
The models are being made in Maya(2013), Exported as .FBX and loaded into XNA. I follow this procedure for exporting: 1. Make Model.
2. Freeze transformation, center pivotpoint and delete history for each part of the model.
3. Combine the mesh and name appropriately.
Example to visualize this. Apparently I can't post images, so here is an Imgur link.
http://imgur.com/a/KHvPU#0
Thanks in advance for your help. This issue happens across more than just this example. I have 5 of each type (wheels, engines, chassis and spoilers), along with separate turbine instances for any models which have them, and other misc. parts. It seems to be totally random from one .FBX file to another... I cant work out if this is a Maya issue, or an XNA issue, or a combination of both :(
Relevant code. This is in a car Class, I have selected the relevant parts.
namespace CGD_RRR_Flipbook
{
//This is a class for the physics, position, color and perhaps race position (i.e. rank) of a car
public class Car : PhysicsObject
{
public string partName;
public int partNumber = 1; //(Initialised for wheel rotation requirements)
public List<string> partList = new List<string>();
//Animation Mesh and Bones Setup
//Chassis
public ModelBone chassis_01 { get; set; }
public ModelBone chassis_02 { get; set; }
public ModelBone chassis_03 { get; set; }
public ModelBone chassis_04 { get; set; }
public ModelBone chassis_05 { get; set; }
//Chassis Turbines
public ModelBone chassis_01_Turbine { get; set; }
public Matrix chassis_01_TurbineTransform { get; set; }
public ModelBone chassis_02_Turbine { get; set; }
public Matrix chassis_02_TurbineTransform { get; set; }
public ModelBone chassis_05_Turbine_Right { get; set; }
public Matrix chassis_05_Turbine_RightTransform { get; set; }
public ModelBone chassis_05_Turbine_Left { get; set; }
public Matrix chassis_05_Turbine_LeftTransform { get; set; }
//Engine
public ModelBone engine01 { get; set; }
public Matrix engine01Transform { get; set; }
public Matrix[] boneTransforms { get; set; }
//Movable Mesh and Bones setup
public int partPosition = 1; //Sets x-position amount
public float wheelRotationValueBase { get; set; }
public float wheelRotationValueUpdate { get; set; }
public float engineRotationValueBase { get; set; }
public float engineRotationValueUpdate { get; set; }
public Car(
ParticleSystem exhaustSmokeParticles,
ParticleSystem exhaustFlameParticles,
ParticleSystem exhaustBoostParticles,
ParticleSystem carDustParticles,
ParticleSystem sandstormParticles,
ParticleSystem explosionParticles,
HUDController _hudController, PlayerIndex _playerIndex, Terrain _terrain, GraphicsDevice _device, Effect _effect, Random randomNumber,
Controls keyBindings, int _player, SoundController _soundcontroller, string fileName = "", ContentManager content = null)
: base(fileName, content)
{
//Load Model
chassis_01_Turbine = model.Bones["Chassis_01_Turbine"];
chassis_01_TurbineTransform = chassis_01_Turbine.Transform;
chassis_02_Turbine = model.Bones["Chassis_02_Turbine"];
chassis_02_TurbineTransform = chassis_02_Turbine.Transform;
chassis_05_Turbine_Left = model.Bones["Chassis_05_Turbine_Left"];
chassis_05_Turbine_LeftTransform = chassis_05_Turbine_Left.Transform;
chassis_05_Turbine_Right = model.Bones["Chassis_05_Turbine_Right"];
chassis_05_Turbine_RightTransform = chassis_05_Turbine_Right.Transform;
chassis_01 = model.Bones["Chassis_01"];
chassis_02 = model.Bones["Chassis_02"];
chassis_03 = model.Bones["Chassis_03"];
chassis_04 = model.Bones["Chassis_04"];
chassis_05 = model.Bones["Chassis_05"];
engine01 = model.Bones["Engine_01"];
engine01Transform = engine01.Transform;
Update Function
public override void update(float dt)
{
//Calls randomiser (once) when player presses key in the generation state
if ((keyState.IsKeyDown(keyBinds.controlsList[player].forward)) && (!oldKeyState.IsKeyDown(keyBinds.controlsList[player].forward))
|| (padState.IsButtonDown(keyBinds.contForward)) && (!oldPadState.IsButtonDown(keyBinds.contForward)))
{
carRandomiser();
}
}
base.update(dt);
}
Draw Function.
public override void draw(Camera cam)
{
model.Root.Transform = worldMat; //sets model root transform to world
float wheelRotationValue = (wheelRotationValueBase + wheelRotationValueUpdate);
float engineRotationValue = (wheelRotationValueBase + wheelRotationValueUpdate);
//Chassis Engine Rotation Animation
Matrix engineRotation = Matrix.CreateRotationZ(engineRotationValue * 20);
chassis_01_Turbine.Transform = engineRotation * chassis_01_TurbineTransform;
chassis_02_Turbine.Transform = engineRotation * chassis_02_TurbineTransform;
chassis_05_Turbine_Left.Transform = engineRotation * chassis_05_Turbine_LeftTransform;
chassis_05_Turbine_Right.Transform = engineRotation * chassis_05_Turbine_RightTransform;
//Wheel Rotation Animation
//Matrix wheelRotation = Matrix.CreateRotationX(wheelRotationValue); //Create rotation Matrix
boneTransforms = new Matrix[model.Bones.Count]; //Creates array for holding modelBone transform matricies for use in draw method.
model.CopyAbsoluteBoneTransformsTo(boneTransforms); //Allocate trasform matricies
if (model != null)
{
foreach (ModelMesh mesh in model.Meshes)
{
//Draw parts assigned to car from partList.
foreach (string part in partList)
{
//Allows only the part in the list to be drawn, as opposed to all the possible parts.
if (mesh.Name == part)
{
effect.EnableDefaultLighting();
effect.PreferPerPixelLighting = true;
effect.World = boneTransforms[mesh.ParentBone.Index];// + worldMat;
effect.Projection = cam.projMat;
effect.View = cam.viewMat;
mesh.Draw();
}
}
}
}
}
}
The randomiser function.
//Car Randomiser Function. Looks for model bones allocated in FBX file.
public void carRandomiser()
{
//Delete contents of list.
partList.Clear();
//Spawn car engine
partNumber = rand.Next(0) + 1;
partName = ("Engine_0") + partNumber.ToString();
partList.Add(partName);
//Spawn car chassis
partNumber = rand.Next(5) + 1;
partName = ("Chassis_0") +partNumber.ToString();
partList.Add(partName);
//Spawn engine turbine for selected engine.
if (partName == ("Chassis_01"))
{
partList.Add("Chassis_01_Turbine");
}
if (partName == ("Chassis_02"))
{
partList.Add("Chassis_02_Turbine");
}
if (partName == ("Chassis_05"))
{
partList.Add("Chassis_05_Turbine_Left");
partList.Add("Chassis_05_Turbine_Right");
}
}
}
}